Here goes my 2 cents
...these are just my opinions from my observations
First, I've never had luck with mixing soils with coco, they both want a different PH for nutrient uptake
Second, If it's more coco than soil, you probably need to water more often, straight coco needs watering with minimal nutes and cal-mag everyday, twice a day, PHed @ 5.6 to 5.8...as long as it's below 6
Third, I never use sand, it's crap for cannabis, it'll compact the soil and cause root bind, not too mention it retains water and will dampen off your roots (root rot)
Fourth, I use my hard ass tap water in my FFOF, I don't PH anything, and I let my girls set in their runoff to soak it back up
RECOMMENDATIONS; Get some Fox Farms soil and quick ...Seriously, I've tried coco, hempy, aeroponics, hydroponics, organics...hell I started in Miracle Grow with CFLs
...I'm still learning, and I don't claim to know everything, or to know the how or why of things, but after 15 years I have a pretty good handle on what works and what doesn't
Proof is in the pics, take a walk through my journals and see for yourself, they're in my sig
...Just a sample...